Hitherto, an engine automatic stop/restart system has been developed for automatically stopping an engine when predetermined conditions are satisfied for the purpose of improvement of the vehicle fuel consumption, reduction in an environment load, and the like. However, it takes time for the engine rotation to be completely stopped by a friction force, and hence there is such a problem that the related-art engine automatic stop/restart system cannot carry out the restart of the engine during this period.
Then, in order to solve the problem, there has been proposed an engine start control device for engaging a rotational drive mechanism with an engine, thereby rotationally driving the engine when it is determined that an engine rotation speed has decreased to a rotation speed allowing the rotational drive mechanism to engage with the engine (for example, refer to Patent Literature 1).
Moreover, there has been proposed an engine automatic stop/start control device for estimating a trajectory of a drop in an engine rotation speed when an engine is to be automatically stopped, and determining, based on estimated data for the engine rotation drop trajectory, a timing of pushing out a pinion gear of a starter to mesh the pinion gear with a ring gear coupled to a crankshaft of the engine (for example, refer to Patent Literature 2).
Moreover, there has been proposed an engine automatic stop/restart device configured as follows. In a case where an engine stop condition is satisfied to stop fuel injection to an engine and thereafter an engine restart condition is satisfied before the engine is stopped, when it is determined that a self-recovery of restarting the engine only by restart of the fuel injection is possible, the fuel injection to the engine is restarted for the self-recovery of the engine. When it is determined that the self-recovery of the engine is not possible, the fuel injection to the engine is restarted, and based on an engine rotation speed and a pinion gear rotation speed, operations of pinion gear drive means for axially moving a pinion gear to mesh the pinion gear with a ring gear and a starter motor for rotationally driving the pinion gear are controlled (for example, refer to Patent Literature 3).